The present invention relates to a rotary torque transmission apparatus for four-wheel drive vehicles, usable as a 2-4 wheel drive change over apparatus for a 4-wheel drive vehicle, and more specifically to a 2-4 drive change over apparatus for a 4-wheel drive vehicle, usable as a gear shift device for automotive vehicle such that 2 wheel drive can be changed over from 2 to 4 wheel drive or vice versa, or a differential lock mechanism provided for a differential gear disposed between wheels can be shifted from a lock status to an unlock status or vice versa in a 4-wheel drive vehicle. Further, the present invention relates to a 2-4 wheel drive change over apparatus provided with a cam switch.
A prior-art 2-4 drive wheel change over apparatus for 4-wheel drive vehicles disclosed in JP Utility Model Kokai Publication No. 60-163120 will be briefly described with reference to FIGS. 9 and 10. The numeral 50 denotes a between-wheel differential gear. The numeral 51 denotes a gear shift device of a differential lock mechanism 49 composed of an input shaft 52, an output shaft disposed in parallel with the input shaft 52, a shift fork 54 for converting the rotation of the output shaft 53 into the axial direction thereof and transmitting the axial movement of the shaft 53, and a slider 59 disposed at a gear engagement portion 58 including splines 56 and 57 of a power train (made up of a ring gear and a pinion carrier 55) of the differential gear, so as to be slidably driven by a shift fork 54.
The input and output shafts 52 and 53 are rotatably supported by a casing 60 at both ends thereof. A worm wheel 61 and a gear 61a are fixed to the input shaft 52. The worm wheel 61 is in mesh with a worm gear 64 fixed to the output shaft 63 of a motor 62 mounted on one-side of the casing 60. A gear 61a fixed to the input shaft 52 is in mesh with teeth formed on a circular arc-shaped end surface of a rotary plate 67a rotatably supported by the output shaft 53.
An end of the output shaft 53 is coupled with a shift rod 65 so as to be rotatable together, while an end of the shift rod 65 is coupled via a helical spline with a cylindrical member 66 on which a shift fork 54 is mounted. Therefore, when the shift rod 65 rotates in the forward or reverse direction, the cylindrical member 66 and the shaft fork 54 are moved to and fro to reciprocably drive the slider 59.
The reference numeral 67b denotes another rotary plate fixed to the output shaft 53 opposite the rotary plate 67a. The numeral 68 denotes a coil spring wound around the output shaft 53 between the two rotary plates 67a and 67b. Another coil spring 69 is wound around the output shaft 53 between the rotary plate 67b and the wall surface of the casing 60. A pin 70 and another long pin (not shown) are provided for the rotary plate 67a so as to support the coil spring 68. In other words, one arm 68a of the coil spring 68 is in contact with the pin 70, and the other arm 68b thereof is in contact with the long pin. On the other hand, one arm 68a of the coil spring 68 is in contact with a pin 71 of the rotary plate 67, and the other arm 68 thereof is in contact with the pin (not shown) of the rotary body 67b. Further, one arm of the coil spring 69 is in mesh with a pin 72 of the rotary body 67b, and the other arm thereof is in mesh with a pin 73 provided for the casing 60.
Under the condition that the slider 59 is engaged with the spline 56 as shown in FIG. 7, when the output shaft 63 of the motor 62 and the worm gear 64 are rotated counterclockwise, the input shaft 52 is driven via the worm wheel 61 in the arrow direction in FIG. 8. Therefore, the rotary plate 67a in mesh with the gear 61a is rotated clockwise, and one arm 68a of the coil spring 68 is urged via the pin 70 clockwise, so that the output shaft is rotated clockwise.
When the coil spring 68 rotates clockwise, the other arm 58b urges the pin (not shown) of the rotary plae 67b in the same direction to rotate the rotary plate 67b and the output shaft 53 clockwise, so that the shift rod 65 is rotated clockwise (in the arrow direction in FIG. 7). When the shift rod 65 rotates in the arrow direction, this rotational movement converts the movement of the cylindrical member 66 into a straight movement via a helical spline to move the shift fork 54 in the rightward direction. Therefore, the slider 59 is engaged with the splines 56 and 57, so that a ring gear (not shown) and the pinion carrier 55 of the between-wheel differential gear 50 are engaged with each other into a lock status in the differential lock mechanism 49.
In the prior-art 2-4 wheel drive change over apparatus, however, since both ends of the coil spring 68 are bent outwardly and further the spring 68 is provided inside the two rotary plates 67a and 67b provided with the pins in contact with both the ends thereof, there exists a problem in that the spring constant of the spring inevitably increases (if the spring size is the same) and therefore it is difficult to determine a necessary torque.
Further, in the prior-art 2-4 wheel drive change over apparatus, since the coil spring 68 is directly wound around the output shaft, when a rotational power is charged by the rotation of the coil spring (torsion spring) beyond 90 degrees, there exists a problem such that the spring is deformed permanently in shape, thus degrading the efficiency markedly.
Further, in the prior-art 2-4 wheel drive change over apparatus, since the coil spring 68 is wound around the output shaft 53 and one arm 68a is in contact with the pin 70 of the rotary plate 67a to obtain an output power from the coil spring, there exist various problems such that a large output is required to change over the apparatus; it is difficult to determine the spring (constant); two coil springs 68 and 69 or a large coil spring is required.
Further, with respect to the prior art 2-4 wheel drive change over apparatus, although there has been proposed one such that a cam switch for detecting the angular position of the worm wheel is provide at the lower part of the worm wheel which applies a rotational torque to the torsion spring, no cam switch covering member is provided.
Since no covering member is provided for the cam switch provided at the lower part of the worm wheel, a rotational force is applied to the worm wheel and grease is applied to the worm gear driven at a high speed by a motor. Therefore, grease is scattered away and stuck onto the cam switch, resulting in another problem such that the change over contact operation is not reliable.